Devices and procedures for production of hydrocarbons from subterranean reservoirs below a seabed have previously been described. In one such procedure, a floating drilling or/and production vessel is positioned above a wellhead on the seabed with a riser extending between the vessel and the wellhead. The riser must be suspended by the vessel at all times in order to prevent it from buckling. Over the years, technological advances have made it possible to extract hydrocarbons from subsea reservoirs at considerable water depths. Today, operations at water depths exceeding 3000 meters are not uncommon.
A marine drilling riser comprises a number of successive sections, which are often referred to as “riser joints”. Individual marine riser joints typically vary in length from 10 to 90 feet (approximately 3 to 27 meters) and are stacked vertically or horizontally on the drilling vessel. During deployment into the sea, with assistance of the vessel's hoisting equipment, the joints are interconnected to form a continuous riser string stretching from a blow-out preventer (BOP) and the Lower Marine Riser Package (LMRP) on the subsea wellhead to the drilling vessel. Depending on water depth, a riser string may consist of only a few joints, or up to more than a hundred individual joints.
A riser joint is typically made up of a main pipe and external auxiliary pipes, all having connectors at each respective end. The main pipe is configured to convey drilling fluid, while auxiliary pipes, often referred to as “kill and choke lines”, are used to circulate fluids between the drilling vessel and the BOP in a manner which is per se well known in the art.
A considerable riser mass must be supported by the floating vessel when operating in water depths of around 3000 meters and beyond. Drilling operators and oil companies therefore always seek to reduce the size and weight of the riser joint components. However, because some of the auxiliary pipes (notably the kill and choke lines) convey fluids that are under considerable pressure, their wall thickness and strength must have a certain magnitude. While riser joint pipes traditionally have been made from various steel grades, in an effort to reduce weight, recent developments have yielded riser joint with pipes made of carbon-reinforced composite materials.
Drilling equipment is normally subjected to elevated temperatures arising from geothermal heating or through circulation of hot hydrocarbons from the reservoir. Although drilling fluid is entered from the top at ambient temperature, the fluid is heated as it circulates through the drill pipe, via the drill bit, and returns back through the well bore. In subsea drilling, the heated drill fluid may in turn heat up the subsea marine drilling riser which is suspended between the BOP, LMRP, and the floating drilling vessel. Depending on the well conditions and the reservoir in question, expected temperatures may exceed the certified temperature rating of the equipment. More heat resistant riser structures and materials are therefore needed for specific operations. The riser auxiliary pipes may also be exposed to elevated temperatures, particularly when circulating out hydrocarbons arising from a kick in the well. Riser joints having pipes made of carbon-reinforced composite materials (for example, carbon-reinforced epoxy) are therefore generally unsuitable for such high-temperature conditions.